Okay so ignore these nerds.
It honestly doesn't matter what server you're on when it comes to playing with friends as you can join each other cross servers for anything. Only problem is factions. You can't be on Alliance and play with Horde. Don't let that deter you either, pick the race you want. If you want to be a panda person, be a panda person. You want to be a Gnome, be a gnome! If you think Cow people are cool, well think you're cool too!
Sargeras is the largest and most popular server for raiding. It's where you get most of your Pro raiding teams. BF is on that one, I'm on a smaller one called Vek'nilash. If you're interested in the economy funtimes then a larger pop server will be better for you.
As for your role, pick one you think you'll enjoy, don't worry about the meta of it. Pretty much every expac, that changes anyway. Unless you're wanting to raid in a hardcore guild, it doesn't matter what class and spec you pick, just have fun.
Cool thing I think you'll end up doing if you stick with it is WoW tokens. They now have it where you can buy wow tokens and that'll pay for your subscription. So you wont have to actually pay for the game, just take the time to get t he money for tokens.
I don't play as much as I used to. I still log on occasionally but I don't raid or anything. I'm more of a lore junkie than anything and it is chock full of it. You'll have a lot to play through for a while as you level which is great. If you do decide to make a character, hit me up and i'll do the recruit a friend thing and run around with you